Recently, destruction of the ozone layer has been concerned. Due to this problem, CFC (chlorofluorocarbons) and HCFC (hydrochlorofluorocarbons) conventionally used as refrigerants for refrigerating machines become subjects to regulation and alternatively HFC (hydrofluorocarbons) has been increasingly used as a refrigerant. In addition, refrigerants having a lower global warming potential (GWP) than HFC refrigerants have been developed (for example, see Patent Literature 1).
In the meantime, in the cases of using conventional CFC and HCFC as refrigerants, a refrigerating machine oil such as a mineral oil and a hydrocarbon oil including alkyl benzene have been suitably used. Since behaviors of a refrigerating machine oil such as compatibility with a refrigerant, lubricity, dissolution viscosity to the refrigerant and thermal/chemical stability vary depending upon the type of refrigerant used in combination and cannot be expected, a refrigerating machine oil must be developed for every refrigerant.